The invention relates to a method for operating a working machine and a working machine.
The invention is applicable on working machines within the field of industrial construction machines, in particular wheel loaders. Thus, the invention will be described with respect to a wheel loader. However, the invention is by no means limited to a particular working machine. On the contrary, the invention may be used in a plurality of heavy working machines, e.g. articulated haulers, trucks, bulldozers and excavators.
Wheel loaders are generally provided with an internal combustion engine, a transmission line, a gearbox, driving wheels and a working hydraulic system.
The combustion engine provides power to the different functions of the wheel loader. In particular, the combustion engine provides power to the transmission line and to the working hydraulic system of the wheel loader.
The transmission line transfers torque from the combustion engine to the gearbox, which in turn provides torque to the driving wheels of the loader. In particular, the gearbox provides different gear ratios for varying the speed of the driving wheels and for changing between forward and backward driving direction of the wheels.
The working hydraulic system is used for lifting operations and/or for steering the wheel loader. For this purpose there are at least one hydraulic working cylinder arranged in the wheel loader for lifting and lowering a lifting arm unit, on which a bucket or other type of attachment or working tool is mounted for example forks. By use of another hydraulic working cylinder, the bucket can also be tilted or pivoted. Further hydraulic cylinders known as steering cylinders are arranged to turn the wheel loader by means of relative movement of a front and rear body part of the wheel loader.
To protect the combustion engine of a wheel loader from sudden rapid changes in the working conditions of the gearbox and the driving wheels it is common to provide the transmission line with a hydrodynamic torque converter or similar arranged between the combustion engine and the gearbox. The hydrodynamic torque converter provides an elasticity that enables a very quick adaptation of the output torque to the changes in the working conditions of the gearbox and the driving wheels. In addition, a torque converter provides an increased torque during particularly heavy working operations, e.g. during acceleration of the wheel loader.
For example, if a wheel loader without the elasticity of a torque converter or similar is driven into an obstacle so that the driving wheels of the vehicle stops this will also stop the combustion engine, since the engine in such designs is rigidly and unyieldingly connected to the rotation of the driving wheels. However, this will not happen if a torque converter or similar is arranged between the engine and the driving wheels or more preferably between the engine and the gear box. On the contrary, if the driving wheels of the wheel loader stops this causes the output side (the turbine side) of the torque converter (the turbine side) to stop whereas the input side (the pump side) continues to rotate together with the engine. The engine will experience a larger internal resistance from the torque converter but it will not come to a standstill.
However, the elasticity of a hydrodynamic torque converter or similar is not present between the working hydraulic system and the combustion engine. On the contrary, the combustion engine provides power to the hydraulic pump or pumps of the working hydraulic system in a more or less direct manner, e.g. by means of a mechanical gear wheel transmission connected between the output shaft of the engine and the input shaft of the pump or pumps. In other words, a rapid increase of the load on the working hydraulic system is transmitted to the combustion engine without any significant attenuation. Naturally, this may cause the combustion engine to stall or cause the power provided by the combustion engine to be fully consumed by the hydraulic system leaving the transmission line without significant power. This may provide an operator of the wheel loader with the highly undesired impression that the engine has become to weak to move the wheel loader in an operable manner. One way of solving the problem of meeting a sudden rapid increase of the load on the working hydraulic system is to run the combustion engine of the wheel loader at the higher end of its speed range. This provides a power margin which makes it easier for the combustion engine to meet a rapid load increase on the hydraulic system, e.g. time to recover by increasing the throttle. However, in general a higher rotational speed leads to significantly increased losses and thus increased fuel consumption. Therefore, with regard to fuel consumption it is better to run the combustion engine at lower rotational speeds.
However, this will give a significantly reduced margin for the combustion engine to recover from sudden rapid increases of the load on the working hydraulic system.
In addition, to ensure that the hydraulic functions are equally fast at the lower rotational speeds, i.e. to ensure the same hydraulic flow at the lower rotational speeds, it is necessary to use larger pumps with higher displacement. A larger pump displacement requires a larger torque from the source driving the pump, i.e. from the combustion engine. In other words, if we move from higher rotational speeds towards lower rotational speeds for reducing losses and fuel consumption we will need hydraulic pumps with a higher displacement, which in turn leads to a higher torque load on the combustion engine. A higher torque load on the combustion engine at a lower rotational speed implies that the engine is utilized even harder. Hence, compared to the utilization at higher rotational speed for powering hydraulic pumps with a lower displacement it has now become even more difficult for the combustion engine to recover from a rapid increase of the load on the working hydraulic system.
Therefore, when designing a modern combustion engine for a working machine such as a wheel loader it is desirable to obtain high output torques at low rotational speeds and to obtain quick reactions on sudden rapid increase of the load on the working hydraulic system. To this end it is common to employ various turbo chargers or air compressors. However, these and other solutions for reinforcing the performance of a combustion engine are commonly in conflict with increasingly harder emission regulations, particularly with respect to exhaustion gases and visible smoke emanating from engine responses to sudden rapid increases of the load on the working hydraulic system. Considering the above there is clearly a need for a working machine provided with an improved and a more flexible ability to meet a sudden rapid increase of the load on the various power requiring and/or torque requiring sub-systems within the working machine.
It is desirable to provide a method for operating a working machine with an improved and a more flexible ability to balance a sudden rapid increase of the load on the various power requiring and/or torque requiring sub-systems within the working machine.
According to an aspect of the present invention, a method is provided for operating a working machine provided with: a power source providing power and a plurality of power consuming systems connected to the power source, characterized by the steps of providing a model predicting a power demanded by at least one of the power consuming systems, detecting at least one operational parameter indicative of a power demand, using the detected operational parameter in the prediction model, and balancing a provided power to the demanded power according to the prediction model. According to a preferred embodiment, the method comprises balancing a provided power to the demanded power so that a load on the power source is reduced.
The prediction model may comprise a characteristic representation of the operative interaction between the power source and the power-consuming systems, such as a mathematical model in the form of for example an advanced dynamic simulation model and/or a less sophisticated equation or system of equations.
The inventive method is preferably utilized in a working machine, in which different power consuming systems are operated simultaneously, such as in a wheel loader. Especially in such an application, it is preferable that the method comprises simultaneously monitoring a demanded power of a plurality of the power consuming systems and correspondingly balancing the power.
Preferably, the power consuming systems comprises a transmission line arranged between the power source and driving wheels of the working machine for transmitting torque from the power source to the driving wheels. Further, the power consuming systems preferably comprises a working hydraulic system comprising at least one hydraulic pump powered by the power source for moving an implement on the working machine and/or for steering the working machine.
According to a preferred embodiment, the method comprises detecting at least one operational parameter indicative of a current working condition of the power source and/or at least one of the power consuming systems. Detecting the operational parameters for these sub-systems (Ae. the power source, the transmission line and the working hydraulic system) creates conditions for providing an earlier indication of the power balance or the coming power balance in a summation point compared to detecting the operational parameters for the summation point, in particularly if the summation point is a fly wheel.
According to a further preferred embodiment, the method comprises detecting at least one operational parameter by detecting at least one input command from a working machine operator. Detecting the commands given to the sub-systems provides an even earlier indication of the power balance or the coming power balance in the summation point. Further, by detecting the operator commands, an accurate prediction of the behaviour of the power source and the power consuming systems may be performed.
Preferably, the method comprises both detection of at least one operational parameter indicative of a current working condition of the power source and/or at least one of the power consuming systems and at least one input command from a working machine operator.
According to a further preferred embodiment of the inventive method, the power consuming systems are connected to the power source via a branching-off portion, and that the prediction model comprises a power summation point, which represents the branching off portion. Thus, the summation point in the prediction model corresponds to a physical point where the power from the power source is divided to the different power consuming systems. In other words, the predicted power to the power consuming systems are subtracted from a predicted power delivered from the power source according to the prediction model. The method preferably comprises balancing the power when the prediction model indicates that the power balance between the power source and the power consuming systems is or will be below zero in the summation point. Further, the method preferably comprises the step of temporarily adjusting the balance until the prediction model indicates a balance condition in which said power is zero or above zero in the summation point.
Said power balancing may be performed in a plurality of alternative and/or contributory ways, such as by adding torque to the transmission line by means of an external power source (such as an electric machine), by effecting the power source and/or at least one of the power consuming systems, and by reducing (such as by scaling down) an actual power provided to at least one of the power consuming systems relative to a demanded power.
Utilizing an external power source is particularly advantageous since this reduces the need for decreasing the performance of the power requiring sub-systems and/or torque requiring sub-systems within the working machine. In addition, the demands on the main power source of the working machine can be relaxed.
The use of at least one electric machine is advantageous, since this enables a flexible and compact design. An electric machine can also be powered by means of a plurality of power sources (e.g. batteries, generators, fuel cells etc), which provides an increased freedom in the design. Moreover, electric machines react fast on commands and they provide a large torque already at low rotational speeds, which is beneficial considering that a rather large torque may have to be supplied fairly fast.
It is preferred that the electric machine is arranged upstream a possible transmission unit arranged in the transmission line, or upstream a possible gearbox arranged in the transmission line. In this way the electric machine does not have to work in both clockwise and counter clockwise directions to accommodate for both a forward and a reverse driving selected by means of the gear box. Moreover, arranging the electric machine upstream the transmission unit enables a more direct torque support to branching-off portion, which in most cases is physically positioned at a point that is located upstream a possible transmission unit.
It is also desirable to provide a working machine with an improved and a more flexible ability to balance a sudden rapid increase of the load on the various power requiring and/or torque requiring sub-systems within the working machine. According to an aspect of the present invention, a working machine is provided with: a power source adapted to provide power and a plurality of power consuming systems connected to the power source, characterized by a control unit which is adapted to predict a power demanded by at least one of the power consuming systems on the basis of at least one operational parameter indicative of a power demand, means for detecting said at least one operational parameter, wherein the detection means is connected to the control unit, and means for balancing a provided power to the demanded power according to the prediction model, wherein said balancing means is connected to the control unit.
The working machine displays the same or similar advantages as the method described above.
Further advantages and advantageous features of the invention are disclosed in the following description.